X-ray tube.



Patented m. 12, 1916.

C. A. FRIEDRICH.

X-RAY TUBE.

APPLICATION FILED JAN.2B, 1914.

CHARLES A. FRIEDRICH, OF NEW YORK, N. Y.

lX-RAY TUBE.

Specification of Letters Patent.

Patented Dee. 1L2,- llfillfi,

Application filed January 28, 1914. Serial No. 814-560.

To all whom it may concern:

Be it known that 1, CHARLES A. FRIED- RICH, a citizen of the Empire ofGermany, and a resident of New York, in the county and State of NewYork, have invented certain new and useful Improvements in X-Ray Tubes,of which the following is a specification.

llhis invention has reference to improvements in vacuum tubes, andpertains par ticularly to X-ray tubes. It also comprises a novel methodof thoroughly exhausting large amounts of metal in such tubes.

It is the special purpose of my invention to produce such X-ray tubesthat will gencrate, in an extremely high vacuum, X'rays of considerablewave length which will produce the finest details of tissues; the glasswalls of my novel tubes remain perfectly cool although they arevery muchnearer the anode than in former tubes; furthermore to devise such means,whereby the very massive electrodes of my new tubes may be thoroughlyexhausted without creating a static field during this process ofexhausting. v

It is well known to science that the wave lengths or penetration powerof X-rays is solely due to the velocity with which the molecules of theresidual gases are carried toward the target, thus forming the cathodalstream. Up to the present time the only factor known to govern thevelocity of these molecules was thedegree of the vacuum,

that is, their velocity lncreases with the increasing vacuum. Butstrangely enough the highly penetrative rays of the former X-ray tubesdo not produce details oftissues such as lungs, stomach, kidneys, etc.On the contrary, such details get lost entirely. Knowing this fact, theX-ray workers have adopted the technique of using X-ray tubes of lowpenetration to insure details, and in order to arrive at shortexposures, they are passing an enormous amount of current through thetube, whereby naturally the former X-ray tubes become defective veryquickly. The fact that the former highly penetrative X-rays do notproduce details,

however, does not coincide with this distinct character of rays of lowerpenetration, because X-rays of even the greatest wave length ought toproduce the finest details,

. owing to the very rnuch shorter exposures.

The practice withthe former tubes of a field will almost out out theaction of the vacuum pump, so that the liberating gases of the metalparts will not only accumulate in the tube, but exist there under acertain pressure; besides, the presence of the static field does notadmit these dense metal gases to remain within same, but they get forcedagainst the glass wall, where they partly condense and so form a minutelining of metallic origin upon said glass walls. Now, if we have such atube highly exhausted, electric leakages along the glass wall occurwhich will impart a secondary motion upon the waves of X-light and somake them lose their original character of producing details of tissues.

In order not to obstruct the action of the vacuum pump and also to avoidthe pres ence of condensed metal vapors upon the glass wall, I havedevised a special method of exhausting tubes by using such other heatsources that do not create a static field in the tube during the timethe metal attains red heat. So, for instance, 1 construct my anodehollow and insert a special electric heater into the hollow space, thusbeing able to heat any amount of metal in a very short time to thedesired degree of heat. To enable me to also exhaust thoroughly thecathode, I make provisions for a heating device for this electrodewhereby I am able to heat the very massive cathode to red heat without.the presence of a static field.

A further advantage ofmy newly devised method of exhausting is the factthat by not using any high potential current during the manufacture ofmy tube, 1 preserve the formation of the path for the cathode dischargefor [the individual wave of the operators generator.

Knowing from experience that two X-ray generators of the same make willnot deliver an identical wave, it is evident that if an cathodedischarge is formed according to discovered that this curing of a tubemeans the manufacturers high potential wave, and .if such a finishedtube is used on different installations, then the path of the cathodedischarge, formed in the manufacture, does not suit the different waveof the operators generator and disturbances will take place within thetube in the form of high potential leakages. These phenomena being thecause that the former new tubes had to be cured or seasoned first, Ihave nothing else than to gradually form a new path for the cathodedischarge with the operators' own high potential Wave.

In experimenting with tubes exhausted by my novel method and in whichthe electrodes were thoroughly exhausted, I found that I could not getthe discharge to readily take place between the anode and the cathode,but it would occur from the part of the electrodes nearest the glasswall along the same.

In exhausting my style of tubes, I took special precautions to-avoid anycondensation of metal vapors upon the glass wall whichwould haveaccounted for the discharge taking place between the electrodes alongthe glass wall. The presence of-this phenomenon, however, without anyperceptible deposit of metallic origin upon the glass wall, has led meto the supposition that the molecules of the residual gases in a vacuumtube are not uniformly distributed, but the molecules nearest the glasswall are rather dense, gradually getting rarer toward the center of thevacuum space. In other words these gas molecules are suspended in thespace concentrically. For this reason I have devised in my new tube anentirely different position for my cathode, that is, I

place that electrode in the center of the vacuum space and so prevent itfrom discharging through the denser gaseous mole cules along the glasswall. By placing the cathode in this position the electric resistancebetween the electrodes will decrease from the cathode toward the anode,quite contrary to the former tubes. This decrease of the resistancetoward the anode is due to the fact that the position of the cathode,being in the rarest vacuum while the anode or target is surrounded byconsiderably denser gases.

The foregoing theory is borne out by the fact that the tubes describedin the last paragraph would not discharge between anode and cathode atfirst, as the electrical resistance of the denser gases along the glasswall is considerably less than that of the much shorter way betweenanode and cathode where the residual gas molecules are extremely rare.However, as soon as both elec- -up the gaseous molecules between theelectrodes, whereby naturally their electric resistance fell below thatof the much longer way through the denser gases along the glass wall.The fact that the metal parts within the tube have been brought to amuch higher degree of heat during the exhausting process is ample proofthat further gases have not been liberated. Furthermore, after the tubecools down, the previous conditions are reestablished, which could nothave been the case if gases would have been liberated by overheating theelectrodes. These tubes are neither provided with any regulating devicethat may absorb any such liberated gases. Further research work has alsoconvinced me that those denser residual gases toward the glass walloffer a considerable resistance to the X-waves and in order to cut downthis resistance as much as possible, I devised a diameter of only twoinches for my new tube. In doing this I provide conditions which willnot admit a large difference of density of the gaseous molecules betweenthe glass wall and the electrodes, consequently the X-waves findpractically no resistance within the tube.

The HbOXe facts show clearly that the path of discharge of the formerX-ray tubesis much too long, considering the enormous resistance of theextremely rare gaseous molecules suspended between the electrodes. Theelectric discharge and the cathodal stream being two distinct phenomena,yet, in the former tubes, parts of their respective paths of motion areforced into the same path and so are bound to disturb each other. Toeliminate this primary disturbance, I entirely separate, in my new tube,the path of discharge from that of the cathodal stream by providing anauxiliary discharge electrode consisting of a metal tube that fits overthe anode proper and extends to within 7 mosses certain potential beforeit will discharge. As the gaseous molecules are started upon their pathby the cathodal discharge, their velocity must be proportional to thepoten ity of the gaseous molecules, I have devised.

a cathode of very large capacityv and as the distance between the anodeand the cathode in my tube is only about one-eighth that of the formertubes, it is evident that this increased cathode potential will admit ofa much more rapid discharge Within this extremely short distance andconsequently carry along the gaseous molecules much faster.

In all these experiments I have found that the desired velocity of thegaseous molecules could only be obtained by the above factors combinedwith an extremely high vacuum and with the metal parts thoroughlyexhausted.

The new tubes of the construction hereinbefore described and thoroughlyexhausted would, even with the considerably lower electric resistanceand the higher cathodepotential, not discharge properly, except byheating the electrodes as before mentioned enormous wave length andconsequently very powerful.

From the foregoing it is evident that even a very short path ofdischarge still oflers too high an electrical resistance in an extremelyhigh vacuum, but by heating both electrodes to a red heat, the residualgases between cathode and anode become heated too whereby the electricresistance falls to the extent where a proper discharge is established.

In these experiments a very strange phenomenon presented itself to me,that is, the more I heated the electrodes, the more current was passingthe tube without changing the potential of the current itself. Also thevelocity of the gaseous molecules and the penetration power of theX-rays in- .creased at the same ratio by applying a higher potential tothe tube. But as there is a rather low limit to the heating of theelectrodes, I have devised a special heating element for the cathodewhich primarily serves to heat the cathode to red heat during theexhausting and also in the finished tube toheat the-gaseous moleculesbetween the electrodes to a point wherethe electric used for the anode.and the Xrays thus generated were of discharge will take place readily.This heating element consists of a spiral filament and is suspended,electrically insulated, from the cathode-and part of it being in such aposition between the electrodes that it will neither interfere with theelectric discharge nor the cathodal stream. As a heating source for thisfilament I use the street current in conjunction with a suitablerheostat thus enabling me to heat the residual gases between theelectrodes to a very fine degree, thereby obtaining X-rays of anydesired wave length. In experimenting with such tubes, I also found thatthe inverse currents set up in high potential generators cannotdischarge between the electrodes but only those impulses of electricenergy will pass the tube that make the cathode the'negative electrode.The cause of this phenomenon is that the molecules of the residual gaseswithin the path of the negative discharge are so highly heated up thatthe low electric resistance thereby established will admit of an easydischarge. However, the heating filament, being a considerable distancefrom the positive discharge electrode, will not heat up the gaseousmolecules within the path of the positive discharge at the moment theanode is made the negative discharge electrode.

In order to make my new tube withstand the terrific impact of theenormously fast moving gaseous molecules, I construct my anode hollow,that is, open to the atmosphere so that it may conveniently be cooled;furthermore, about two pounds of metal are Of late X-rays are being usedextensively for the treatment of malignant diseases and to prevent thesuperficial tissues from getting injured, filters of aluminum are usedoutside the tube, so as to prevent the dangerous rays of. a short wavelength to reach. the patient. In my new tube I make use of the auxiliaryanode first to protect the operator from the ill effects of theextremely powerful rays, and secondly, to filter the X- waves within thetube by means of a suit able metal window, thus my new tube can be usedwithout further precautions for treatment work. For X-ray treatment itis also desirable that thetube be brought very close to the patient andas I have for other reasons devised a very small diameter for my tube, Ican safely bring the glass wall of my tube in actual contact with thepatients body, especially as the glass wall remains absolutely cool. Intreating malignant diseases with the glass wall of my new tube in actualtouch with the patients body, I obtain very efiective therapeuticvalues.

In order to render the invention entirely olear'reference is had to theaccompanying drawing 1n''wh1ch:

v Figure 1 represents 1n longitudinal elevadescribed hereinafter.

tion, partly in section, an X-ray tube embodying in desirable form thepresent improvements. Fig. 2 shows in longitudinal section, on anenlarged scale, the cathode with portion broken away. Fig. 8 illustratesin elevation, partly in section, a water cooling device. Fig. 4!represents a special heating device in longitudinal elevation.

Similar characters of reference denote like parts in all the figures.

In the drawing, in Fig. 1 a represents a somewhat compressed glass bulbin which the curved large top portion 1) of the oathode, constitutingthe discharge electrode, is located. The lower narrower portion 6 of thecathode extends into the tube a joined to the bulb a. The tube a isconsiderably less in diameter than the bulb a and has on its lowerportion a tubular lateral extension 0 which is provided for the purposeof introducing the feed wires 03 of a special heating device locatedwithin the cathode and to be Atthe lower end of the tube 0 a narrowertube 6 is joined which houses a tightly fitting split metal tube,preferably a split steel tube f. This tube acts as a substantial supportfor the entire massive cathode. To the bottom end of the tube f issoldered or brazed a substantial lead wire 9 which in turn is fused to aplatinum wire 72. that passes through the rounded off bottom portion ofthe glass tube 6.. A narrow glass tube 71 is fused to a somewhat widerglass tube j. In these "tubes the entire anode mechanism is mounted bymeans of a split steel tube is and the tube j is then joined to the topportion of the glass bulb a.

The massive cathode preferably is made of aluminum. The cathode hascentrally a bore or opening 6 in which part of the special heatingdevice is located. This mecha nism is shown on an enlarged scale in Fig.2 and comprises the heating device connected to the leads d which leadsare held separate by some solid glass 01 fused around the same.

The, leads connect with a spiral filament Z made of some metal of avhigh fusion point,

such as platinum, tungsten and the like. One of the leads is surroundedby an insulating glass tube m and therefore will prevent the lead wiresfrom forming a short circuit. Both leads are separated from the innercathode walls by a silica tube 92. on the upper portion of which thespiral Z is wound. A small split steel tube 0 is mounted in the lowerportion of the cathode by means of a bent wire 0 as shown. Said steeltube 0 serves as a support for the whole heating device. The leads (1being held apart by means of an insulating glass tube m require twosmall openings in-the silica tube 12. for the purpose of rendering itpossible to connect said leads to the free ends of the spiral Z.

The anode ismounted bymeans of the 1,2os,1es

glass tube 2' as previously stated. The anode body ;0 is provided at itslower end with two rings 9 shrunk thereto. Centrally on the slantingsurface of the bottom end of the anode there is a block of silver 1"faced with platinum. To prevent the crossing of the electric dischargeand the cathodal stream these are separated by providing an auxiliarydischarge electrode in form of a'metal tube 8 that is secured to theanode proper and reaches down to about one-half an inch from thecathode. This auxiliary electrode is provided with sharp points 7'. Toeffect the filtration of the X-rays within the tube a metal window 8 isprovided in the tube 8 in the path of the active rays. The short pathfor the electric discharge thus created is adapted to increaseconsiderably the velocity of the gaseous molecules. The anode isconstructed hollow for reasons hereinbefore stated, that is, it is opento the atmosphere and may conveniently be cooled by means of a coolingdevice illustrated, on an enlarged scale, in Fig. 3. This devicecomprises a tube t through which the water flows into the hollow "anode.This tube has a small spiral t at its bottom contacting with the blockof silver 7" of the anode. when inserted, and the 'upper end of thespiral t extends into the copper loop 25 The water flows through thehollow anode and leaves through the tube 8 This arrangement is tightenedwithin the anode by means of a rubber stopper a. In order to close theinner space hermetically a platinum ring o connecting with the anodebody has fused around its upper surface glass from both sides and isjoined to the top of the glass tube 2' in the usual manner. This watercooling device may be conveniently removed and inserted because it isheld in position solely by the rubber stopper M. This device is usedonly for prolonged treatment. For radiographic purposes, for instance,this device is replaced by a mere contact spring slipped into the hollowanode. For the purpose of creating an extremely high vacuum the anodealso is heated during the process of exhausting the same. Such a specialheating device is illustrated, on an enlarged scale, in Fig. 4. Itcom'prisesan insulating tube m with heating spiral m which iselectrically heated by means of'the leads 3 of which the lead 3 isinsulated until it reaches the spiral :11. may be placed into the hollowanode during exhaustion in the same manner as the water cooling device.In this way a thorough exhaustion of the metal is efiected. This heatingof the anode, which is composed of about two pounds of metal, insures aperfect expelling of allthe gases therefrom, that is,

the metal is thoroughly exhausted.

I claim as my invention: 1. The method of expelling the gases in splitsteel tube which fits closely into the X-ray tubes which consists in theproduc- This device.

tion of heat within the hollow anode and cathode, thereby avoiding thecreation of a static field during the periods of time when the metalparts of both electrodes attain a red heat.

E2. The method of expelling the gases from large amounts of metal inX-ray tubes dur ing evacuation which consists in the production of heatwithin the hollow anode and cathode, thereby avoiding the creation of astatic field during the periods of time when the metalparts of bothelectrodes attain a red heat and efiecting thereby a thorough exhaustingof the large amounts of metal of which the electrodes are composed.

3. The method of expelling the gasesin X-ray tubes which consists increating the cathode discharge from the center of the vacuum space andproducing heat within the hollow anode and cathode thereby avoiding thecreation of a static field during the periods of time when the metalparts of both electrodes attain a red heat.

4. The method of expelling gases in X- ray tubes which consists increating a very short path for the electric discharge, starting thecathode discharge from the center of the vacuum. space and producingheatwithin the hollow anode and cathode thereby avoiding the creation ofa static field during the periods of time when the metal parts of bothelectrodes attain red heat.

5. The method of expelling gases in X- ray tubes which consists increating a cathodal discharge, from the center of a large surface andover a very short path, starting the said-cathode discharge from thecenter of the vacuum space whereby uniform conditions are created bothfor the cathode an anode discharges. i

6. The method of operating X-ray tubes which consists in starting thecathode dis charge from the center of the vacuum space and producingheat within the hollow anode and cathode thereby heating the gaseousmolecules in the path of the electric discharge to facilitate the saiddischarge and thus avoiding a partial discharge along the glass wall.

7; The method of operating X-ray tubes which consists in creating a.very short path for the electric discharge starting the cathodedischarge from the center of the vacuum. space and producing heat withinthe cathode thereby heating the gaseous molecules in the path of thecathode discharge to facilitate the said discharge and thus avoiding apartial discharge along the glass wall.

8. The method of operating X-ray tubes which consists in creating acathodal discharge from the center of a large surface and over a. shortpath, starting from the center of'the vacuum space and producing heatwithin the hollow cathode thereby heating the gaseous molecules in thepath ot the cathode discharge to facilitate the said dis charge thusavoiding a negative charge on the glass wall.

9. The method of operating X-raytubes which consists in starting thecathode discharge from the center of the vacuum space and producing heatwithin the cathode and somewhat beyond the latter toward the anodethereby heating the gaseous molecules in the path of the cathodedischarge to facilitate the said discharge and thus avoiding a negativecharge on the glass wall.

10. The method of operating X-ray tubes which consists in creating avery short path for the electric discharge, starting the cathodedischarge for the center of the vacuum space and producing heat withinthe oathode and somewhat beyond the latter toward the anode therebyheating the gaseous molecules in the path of the cathode discharge tofacilitate the said discharge and thus availding a negative charge onthe glass wa 11. The method of operating X-ray tubes which consists increating a cathodal discharge from the center of a large surface 'over ashort path, starting from the center of the vacuum space and producingheat within the cathode and somewhat beyond the latter toward theanodethereby heating the gaseous molecules in the path of the cathodedischarge to facilitate the said discharge and thus avoiding a negativecharge onthe glass wall. 7

12. The method of operating X-ray tubes which consists in separating theelectric discharge from the cathodal stream and creating a very shortpath for said electric dis charge whereby interference with the lengthof the path of the cathodal stream is avoided and the velocity of thegaseous molecules increased. c

13. The method of operating X-ray tubes which consists in separating theelectric discharge from the-cathodal stream and dividing said electricdischarge into a multiple of separate discharges over a very short pathwhereby interferencewith the length of the path of the cathodal streamis avoided and the velocity of the gaseous molecules increased. I

14. The method of operating X-ray tubes which consists in separating theelectric discharge from the cathodal stream, dividing said electricdischarge into a multiple of separate discharges over a very short path,and producing the cathode discharge from a large surface increasingthereb the cathode potential considerably, sai in creased cathodepotential eflecting very rapid cathode discharges and, also, imparting avery much higher motion to the residual gaseous molecules forming thecathodal stream.

15. The method of operating X-ray tubes which consists in separating theelectric discharge from the cathodal stream, dividing said electricdischarge into a multiple of separate discharges over a very short path,and producing the cathode discharge from a large surface increasingthereby the cathode potential considerably, said increased .cathodepotential effecting very rapid cathode discharges and, also, imparting avery much higher motion to the residual gaseous molecules forming thecathodal stream and heating the gaseous residue between the electrodesto form a conductive bridge.

16. An X-ray tube comprising a massive cathode with large dischargesurface,and an anode with an auxiliary discharge device having amultiple of pointed ends located in close proximity to the dischargesurface of the cathode. p

17 An X-ray tube comprising a massive cathode with large dischargesurface and having a central bore, an electric heating device located insaid bore of the cathode for the purpose of facilitating the cathodedischarges. V

18. An X-ray tube comprising a massive cathode with large dischargesurface and having a central bore, an electric heating device located insaid bore of the cathode for the purpose of lowering the electricalresistance between anode and cathode and of heating up the residualgaseous molecules .forming the cathodalstream.

said heating device being adapted to heat the cathode from inside durinexhaustion and to heat the residual gas m0 ecules within the path of thecathode discharge during operation.

20. A vacuum tube having a very massive anode and cathode close to andsubstantially at the same distance from all the adjoining glass wallportions with the cathode in the center of the vacuum space, and meansfor heating the electrodes by a low potential current to preventcreation of the static field to greatly expand and diminish theresiduary gaseous molecules whereby a rather uniform density of gaseousresidue is produgiad between the electrodes and the glass wa Signed atNew York, N. Y., this 27th day of January, 1914.

CHARLES A. FRIEDRICH. Witnesses:

MARIE R. LEAHY, ELIZABETH KRAMER.

